1. Field of the Invention
The invention relates to an improved flap valve for controlling a gas flow through a conduit.
2. Description of the Prior Art
In a known flap valve disclosed in DE 199 34 113 A1, the valve tube that conveys the gas flow is embodied as an elastically deformable thin-walled tube and the valve flap disposed in the valve tube is embodied as a rigid, circular disk. The flap shaft actuating the valve flap encloses an angle α with the valve tube axis of between 10° and 90°, preferably 45°. This embodiment of the flap valve allows the valve tube to be embodied without a through opening for the drive shaft. If the outer diameter of the valve flap is equal to the inner diameter of the valve tube, then the flap normal coincides with the axis of the valve tube. However, if the valve flap has an outer diameter greater than the inner diameter of the valve tube, then in the closed position of the valve flap, this results in an acute angle between the flap normal and the axis of the valve tube, the so-called opening angle. This opening angle is larger, the greater the diameter difference between the outer diameter of the valve flap and the inner diameter of the valve tube is. In the closed position of the valve flap, this diameter difference causes the valve tube to deform into an ellipse whose larger radius corresponds to the radius of the valve flap. When the flap valve is open, the valve flap only contacts the valve tube at two points.
With this structural design of the flap valve, it has turned out that as the angle between the valve tube axis and the flap normal decreases, i.e. as the oversizing of the diameter of the valve flap in relation to the inner diameter of the valve tube decreases, the risk of the valve flap becoming jammed in the valve tube increases. On the other hand, in a valve flap that is oversized to a large degree, the pressure load in the valve tube also causes the thin-walled tube in the closed position of the valve flap to recover to a circular tube and thus causes the valve tube to exert powerful radial forces on the flap edge of the valve flap, which restricts the movement of the valve flap. The permitted angular range for a positioning of the valve flap in relation to the valve tube axis is therefore relatively small.